Oxidation of SO 2 by O 2 and Its Effects on Dithionate Formation during Pyrolusite Leaching Process with Mixture Gas Containing SO 2 and O 2

Competitive oxidations of SO 2 oxidized by MnO 2 and O 2 are existed during pyrolusite leaching process with SO 2 and O 2 mixture gases. Generally, SO 2 is oxidized into H 2 SO 4 by O 2 , and manganese sulfate (MnSO 4 ) and manganese dithionate (MnS 2 O 6 ) are formed when oxidized by MnO 2 . Meanwhile, the reaction between SO 2 and O 2 has effect on the amount of aqueous SO 2 oxidized by MnO 2 and solution acidity, resulting in the variations of Mn extraction and MnS 2 O 6 formation. In this paper, the competitive mechanism of SO 2 oxidation by MnO 2 and O 2 was firstly discussed based on theoretical analysis of leaching process, and then concentration ratio of O 2 /SO 2 ( R ) in gas flow was proposed as a determined parameter to characterize the competition, the effects of R on Mn extraction, H 2 SO 4 generation and MnS 2 O 6 formation. The results showed that R was the determined parameter for evaluating the oxidation effect of O 2 on SO 2 , which had a decisive effect on H 2 SO 4 concentration, and eventually affects MnS 2 O 6 formation and Mn extraction under constant gas flow (10 L⋅min −1 ) and others experimental factor. With the increase of R , the H 2 SO 4 concentration increased gradually but the formation of MnS 2 O 6 sharply decreased to negligible amount when R >10, and Mn extraction increased first and then decreased significantly. The most suitable R for obtaining MnSO 4 product was R =10 with 1.4 g⋅L −1S 2 O 6 2 -, 96% Mn extraction and 0.07 M H 2 SO 4 .